1. Field of the Invention
The present invention relates to a temperature-compensating thin-film capacitor in which temperature dependence of a junction capacitance of a semiconductor is reduced, and to an electronic device that includes the capacitor having reduced temperature dependence.
2. Description of the Related Art
A thin-film capacitor generally has a structure wherein a lower electrode, a dielectric layer, and a upper electrode are deposited on a substrate. Alternatively, a thin-film capacitor can have a structure wherein a dielectric layer, followed by an upper electrode are sequentially deposited on a semiconductor substrate. In some cases, the semiconductor substrate functions as a lower electrode.
The following characteristics are required for the above capacitor: a large Q factor, a large specific inductive capacity, and a small capacitance-temperature coefficient. The capacitance-temperature coefficient may be positive or negative, but is preferably near xe2x80x9c0xe2x80x9d at the resonance frequency.
Conventional dielectric ceramics having the above characteristics are fired BaOxe2x80x94TiO2-based dielectric ceramics which contain samarium oxide (Sm2O3), gadolinium oxide (Gd2O3), dysprosium oxide (Dy2O3), europium oxide (Eu2O3), or the like. However, the specific inductive capacity ∈r is controllable only in the range of 61 to 72 and the temperature coefficient xcfx84 is controllable only in the range of xe2x88x9224 to 31 ppm/xc2x0 C. by conventional technology for producing dielectric ceramics.
Technology development has been conducted in the above background, resulting in a dielectric ceramic laminate formed by the lamination of a first dielectric ceramic sheet having a positive temperature coefficient at a resonance frequency and a second dielectric ceramic sheet
The dielectric ceramic laminate is provided by performing the following steps: producing the first dielectric ceramic disk by preparing a raw material having a desired composition, forming the material into a disk having a diameter of 16 mm and a thickness of 9 mm, and then firing the sheet at 1,260 to 1,450xc2x0 C. for several hours; producing the second dielectric ceramic disk having the same size as the first one by forming and then firing a raw material having another composition; cutting both disks into sheets each having a thickness of 1 mm; and then laminating the sheets.
The dielectric ceramic laminate has a desired specific inductive capacity and a desired temperature coefficient. This is accomplished by laminating dielectric ceramic sheets having different volumes, but the same specific inductive capacity. The desired specific inductive capacity and a desired temperature coefficient of the dielectric ceramic laminate may also be achieved when the laminated dielectric ceramic sheets have different specific inductive capacities.
The above method can provide a capacitor composed of laminated sheets but can not provide a thinner and lighter one because the capacitor is produced by laminating a plurality of sheets including a first dielectric ceramic sheet and a second dielectric ceramic sheet which both having a thickness of about 1 mm. Thus, it is difficult for known methods to form a capacitor having a thickness of 1 mm or less.
To achieve the foregoing and other objects of the invention, the present invention provides a thin-film capacitor which is smaller, thinner, and lighter than a conventional one, and further has improved temperature compensation by using dielectric materials which have a low specific inductive capacity and of which temperature dependence is controllable.
In an embodiment of the present invention a thin-film capacitor is provided which has the above characteristics and a large Q factor at a high frequency of 1 GHz or more. In other embodiments an electronic device is provided which is resistant to changes in temperature, in which the device comprises the thin-film capacitor having the above characteristics.
In other aspects of the present invention, a thin-film capacitor having a negative capacitance-temperature coefficient of which the absolute value is 200 ppm/xc2x0 C. is provided by using a material having a linear thermal expansion coefficient of 25 ppm/xc2x0 C. or more.
In some embodiments, a thin-film capacitor having excellent performance is provided by using a dielectric thin-film having a specific inductive capacity of 4.0 or less and a linear thermal expansion coefficient of 25 ppm/xc2x0 C. or more. The dielectric thin-film has a reduced difference in capacitance in processing and has a large Q factor at a high frequency. Also, miniaturizing, thinning, and lightening the capacitor having a function of temperature compensation is achieved.
In other embodiments, the temperature-compensating thin-film capacitor includes a dielectric thin-film placed between a pair of electrodes, in which the dielectric thin-film has a specific inductive capacity of 4.0 or less and a linear thermal expansion coefficient of 25 ppm/xc2x0 C. or more. Accordingly, the thin-film capacitor is hardly affected by processing accuracy, and has a small difference in capacitance. Also, miniaturizing, thinning, and lightening the capacitor for temperature compensation are achieved.
In yet other embodiments a thin-film capacitor is provided having a Q factor of 100 or more at a high frequency of 1 GHz or more exhibits a small dielectric loss at a high frequency. Accordingly, the thin-film capacitor is suitable for a circuit for a high frequency of 1 GHz or more.
In some embodiments, the dielectric thin-film of the present invention contains a fluoric polymer as a main component and exhibits a specific inductive capacity of 4.0 or less and a linear thermal expansion coefficient of 25 ppm/xc2x0 C. or more. Also, the thin-film capacitor including the film placed between the electrodes exhibits a Q factor of 100 or more at a frequency of 1 GHz or more, according to the kind of the fluoric polymer.
In other embodiments, the dielectric thin-film of the present invention contains a benzocyclobutene polymer or a naphthocyclobutene polymer as a main component, and has a specific inductive capacity of 4.0 or less and a linear thermal expansion coefficient of 25 ppm/xc2x0 C. or more. Also, the capacitor including the film placed between the electrodes has a Q factor of 100 or more at a frequency of 1 GHz or more, according to the kind of the benzocyclobutene or naphthocyclobutene polymer. In this embodiment, the benzocyclobutene polymer and the naphthocyclobutene polymer provide corrosion resistance against a resist-developing solution and a resist-peeling solution used for forming electrodes. Accordingly, the dielectric thin-film composed of the polymers is advantageous with regard to corrosion resistance.
In a device embodiment, an electronic device is provided, which includes the temperature-compensating thin-film capacitor of the present invention, in which the electronic circuit of the device requires a temperature compensation. Accordingly, electronic devices, such as a portable electronic device and microwave communication equipment, including the above electronic circuit is resistant to changes in temperature.